/// <summary>
/// Returns Aho-Corasic tree for a set of patterns and alphabet parameters
/// </summary>
/// <returns></returns>
public static AhoCorasickTree GetAhoCorasickTree(this char[][] patterns, char minChar, char maxChar)
{
var tree = new AhoCorasickTree(patterns.Sum(p => p.Length) + 1, maxChar - minChar + 1, minChar);
foreach (var pattern in patterns)
{
tree.AddString(pattern);
}
return(tree);
}
/// <summary>
/// Counts the number of matchings of patterns in a given text
/// tree must be built with a set of distinct patterns!
/// </summary>
public static long CountMatches(this AhoCorasickTree tree, char[] text)
{
if (text == null || text.Length == 0)
{
return(0);
}
long res = 0;
var dp = new int[tree.Size];
dp.Fill(-1);
dp[0] = 0;
var st = 0;
var stack = new int[tree.Size];
int sz = 0;
for (int i = 0; i < text.Length; i++)
{
st = tree.GetNextState(st, (char)(text[i] - tree.MinChar));
int u = st;
while (dp[u] == -1)
{
stack[sz++] = u;
u = tree.GetSuffixLink(u);
}
while (sz > 0)
{
var cur = stack[--sz];
dp[cur] = (tree.IsLeaf(cur) ? 1 : 0) + dp[u];
u = cur;
}
res += dp[st];
}
return(res);
}
